On the new page scroll down to the “Add New Photo” button, click it, and follow the instructions. Title and description are optional. I believe the default license is Creative Commons (Attribution) but it should tell you if it’s something else. You can select a different license from the drop-down menu if you want.

Once you’ve selected the photo’s location on your computer, click “Upload” and it should take only a few seconds to a minute or so, depending on the speed of your Internet connection.

If everything’s working properly a thumbnail will then appear on the theater’s photos page. Your photo won’t appear on the theater’s main page unless and until it gets enough views to displace the one that’s showing now.